Cobalt oxide catalyst

ABSTRACT

THE SINTNERING OF COBALT OXIDE CATALYST IS FACILITATED BY THE USE AS SINTERING AID OF FROM 1 TO 10% BY WEIGHT OF A CARBOXYLIC ACID SELCTED FROM FUMARIC ACID AND COMPOUNDS OF THE FORMULA R-CO2H WHERE R IS PHENYL, PMETHOXYPHENYL, P-TOLYL, O-HYDROXPHENYL OR DIPHENYLMETHYL, SINTERING BEING EFFECTED AT A TEMPERATURE ABOVE 500*C.

United States Patent US. Cl. 252-459 3 Claims ABSTRACT OF THE DISCLOSUREThe sintering of cobalt oxide catalysts is facilitated by the use assintering aid of from 1 to by weight of a carboxylic acid selected fromfumaric acid and compounds of the formula R-CO H where R is phenyl,pmethoxyphenyl, p tolyl, o hydroxyphenyl or diphenylmethyl, sinteringbeing elfected at a temperature above 500 C.

This invention relates to catalysts, more especially to sintered cobaltcatalysts, to methods for their preparation and to their use in thesynthesis of organic compounds.

It is already known to use reduced cobalt oxide catalysts in thesynthesis of organic compounds, more particularly in the reduction oforganic compounds with gaseous hydrogen and especially in so reducingorganic nitriles to organic amines. An important instance is thereduction of adiponitrile t0 hexamethylene diamine which may be eflected in the liquid phase under pressure by means of hydrogen in thepresence of ammonia and a reduced cobalt oxide catalyst at a temperaturewhich, for example, be in the range 50-200 C. The reduced cobalt oxidecatalyst is obtained by pre-reducing a cobalt oxide catalyst, forexample by heating in an atmosphere of hydrogen, optionally diluted withan inert gas such as nitrogen, at a temperature within the range 100 to400 C.

The cobalt oxide catalyst is normally used in particulate form, forexample in pelleted form, and is previously sintered in order toincrease the physical strength of the catalyst particles, so prolongingthe effective life of the catalyst by inhibiting physical breakdown ofthe catalyst during use. It is known to treat the catalyst particleswith certain substances which act as sintering aids and improve thefinal strength of the particles. Such substances may also act aslubricants in, for example, the pelleting operation which may precedesintering. It is known to use glyceryl tristearate as such a sinteringacid. It has also been proposed to use animal and vegetable stearins,and the higher fatty acids of chain length greater than C and theiresters, especially the esters with polyhydric alcohols such as glycoland glycerol.

It has also been proposed to use in the conversion of adiponitrile tohexamethylene diamine a reduced cobalt oxide catalyst, the activity ofwhich has been increased by incorporation therein of a proportion, forexample 0.1 to 0.5%, of silica. We have now found that improved sintered cobalt oxide catalysts may be obtained by the use of selectedunsaturated carboxylic acids as sintering aids.

According to our invention we provide a process for the manufacture of asintered cobalt oxide catalyst which comprises mixing cobalt oxide inparticulate form with from 1 to 10% by weight of a carboxylic acid whichis fumaric acid or a compound of the formula R-CO H in which R isphenyl, p-methoxyphenyl, p-tolyl, o-hydroxyphenyl or diphenylmethyl, andsintering at a temperature above 500 C.

The particulate cobalt oxide used in our invention may be obtained bycalcining the cobalt carbonate or basic cobalt carbonate precipitatedfrom a solution of a water- 3,829,393 Patented Aug. 13, 1974 solublecobalt salt. Cobalt nitrate may be used as the water-soluble cobalt saltand precipitation may be effected by addition of, for example, ammoniumcarbonate. After drying the cobalt carbonate, calcination to the oxidemay be effected at a temperature within the range to 500 C., for exampleat a temperature of 400 C. for 3 hours.

At this stage it is convenient to increase the density of the solidcobalt oxide, and one method of doing this is to wet-knead the oxide ina kneading machine followed by drying. If desired the cobalt oxide maythen be granulated. By this means cobalt oxide granules having a bulkdensity greater than 1.0 g./ml., for example 1.0 to 1.8 g./ml., and morespecifically 1.4 to 1.6 g./ml., may be obtained, and these areparticularly suitable for use in the process of our invention. Thegranules may be of such a size as to pass a 2 mm. screen or possibly a 1mm. screen, though larger particles may also be used. It is alsopossible, however, to effect increase in density of the solid cobaltoxide by other means, for example by roll compaction or by slugging.

The cobalt oxide may be shaped prior to sintering, for example it may bepelleted. If a shaping operation is adopted it is usually advantageousto mix the cobalt oxide with the carboxylic acid sintering aid prior tothe shaping operating since the said acids act as lubricants during theshaping operation, and this use of the said acids forms a subsidiaryfeature of our invention.

The mixing of the cobalt oxide with the carboxylic acid sintering aid isconveniently effected in the solid state and any conventional mixingmethod may be used, for example, by tumbling in a mixing skip.

The amount of the said :acid may be from 1 to 10% by weight, calculatedon the Weight of the cobalt oxide, and is preferably from 3 to 5% byweight.

Pelleting may be effected in a conventional pelleting machine. It isalso possible to use shaped cobalt oxide in ball form. Although shapedcobalt oxide may be used in a wide variety of shapes and sizes, weprefer to use pellets, for example, cylindrical pellets, in the sizerange inch to inch) x inch to% inch).

After mixing the cobalt oxide with the carboxylic acid sintering aid itis sintered by heating at a temperature above 500 C. Temperatures ofsintering are normally in the range 500 to 1000 C., and preferably inthe range 600 to 750 C. Generally speaking the lower the temperature ofsintering the longer the time required, but the time usually variesbetween /1 hour and 12 hours. Sintering may, for example, be effected bypassing the pellets continuously through a heated furnace. Typically thetime of passage through the heated zone at a temperature of 650 to 700C. will be /2 hour. During the sintering operation the bulk density ofthe cobalt oxide particles is increased, they acquire the desired porestructure and the crush strength is increased. The bulk density isnormally greater than 1.8 g./ml., usually in the range 1.8 to 3.2 g./ml.and preferably in the range 2.0 to 2.5 g./ml.

Compared with particulate cobalt oxide which has been sintered aftermixing with glyceryl tristearate as a sintering aid, the sinteredparticulate cobalt oxide obtained by the process of our invention has ahigher crush strength and is equally effective when reduced and used asa catalyst in the conversion of adiponitrile to hexamethylene diamine.Although it is possible to improve the crush strength of particulatecobalt oxide sintered with glyceryl tristearate as sintering aid byincreasing the bulk density, for example by increasing the temperatureor time of sintering, this results in a diminution in the activity ofthe reduced catalyst in the manufacture of hexamethylene diamine.Particularly valuable carboxylic acid sintering aids of our inventionare benzoic acid and salicylic acid.

It is also possible to apply the process of our invention to themanufacture of sintered cobalt oxide catalysts,

of a proportion of silica, usually 0.1 to 0.5% by Weight calculated onthe weight of the cobalt oxide. In the manufacture of such catalysts itis preferred to add colloidal silica to aqueous cobalt nitrate solutionprior to precipitaing was effected at 800 C. for /2 hr. to give acatalyst of higher crush 's'tr'eng'thbut' r'educed activity. Thephysical characteristics of the catalyst are given in the followingTable. The activity of the catalyst in the reduction of adiponitrile wasassessed as inExample 2.

tion of cobalt carbonate. The subsequentsteps in the man- 5 I, EXAMPLE 5ufacturing operation are then as previously described. The v colloidalsilica may be obtained, for example, by adding PIQPQI f Ca a y t) an forexample nitric a m an 'i fl Q of Granulated cobalt oxide containing 2%of its of a slhcate P example sodlPm metaslhcate- F 9 1O colloidalsilica, and of bulk density 1.5 g./ml.-and pa-rticle promoted sinteredcobalt oxide catalysts of our invention Size less than 12 mesh (BS5) wasmixed -E i have a higher crush strength than silica promoted cobalt i hf b oic acid, the mixture pelleted and the pelox de catalysts sinteredwith glyceryl tristearate as a s1nlets sintered as described inExampl'LThe physical chap terlng 31d, but fi equally CffQCtWe whet} d cand used acteristics of the catalyst are given in the" fol'lowing'Table.as a catalysl the converslon of adlpommle to 15 The activity of thecatalyst in the reduction of adiponitrile f F- was assessed as inExample 2'.

The lnvention 1S lllustrated but not limited by the following Examplesin which the parts and percentages are EXAMPLE 6 by weight. 7

EXAMPLE 1 Comparative Example Preparatlon of catalyst The method ofExample'S was repeated exceptthat the Granulated cobalt oxide of bulkdensity 1.6 g./ml. and silica-containing granulated-cobalt oxide wasmixed with pa cle s s than 12 mesh Was mixed With 3% 3% of its weight ofglyceryl tristearate. The physical charof its weight of b nz i i y m lig i a mixing p acteristics of the catalyst are givenin the followingTable. for 1 hr. The so-treated cobalt oxide was then pelleted to 1 1 yw give pellets of average size 4 inch x inch. The pellets EXAMPLE 7 werethen sintered by passing continuously through a heated furnace, the timeof passage through the heated Preparation of Catalyst zone at 670 C.being A. hr. The physical characteristics of the catalyst are given inthe following Table, The method of Example 1 was repeated .except.thatthe granulated cobalt oxide was mixed with 3% of its weight EXAMPLE 2 ofp-anisic acid. The physical characteristics of thecat- U f c t l t alystare given in the following Table. The catalyst pellets (21.4 g.)prepared as in Example EXAMPLE 1 were charged to a container and thecatalyst reduced by heating at 350 to 400 C. for 3 hours, in anatmosphere The method f Example 1 was repeated 'Xcept h 'flof hydrogenThe Pellets were cooled to below and granulated cobalt oxide was mixedwith 3% of its'weight discharged into methanol before transfer to areactor to f f i acid and sintering was eflected r 2 if which 214 g. ofadiponitrile and 139 g. of ammonia were 40 at 0 I also added. Thereactor was filled with hydrogen to a pres- EXAMPLE 9 sure of 130 ats.and then heated to a temperature of 1' giving a maXimum Pressure ofabout 0 3158- The The method of Example 1 was repeated except that thefate of hydrogen uptake was mfiasufed Over 21 Period of 2 granulatedcobalt oxide was mixed with 3% of its weight hrsand gav a measure of thecatalyst activityof salicyclic acid and sintering was effected for 30iniris'.

at 690 C. i EXAMPLE 3 EXAMPLEIO I Comparative Example The method ofExample 1 was repeated except that the The method of Example 1 rep?atedx h granulated cobalt oxide was mixed with 3% of its weight gram'flatedcoba'lt oxfde was f h o Its Welght of glyceryl tristearate. The physicalcharacteristics of the dlphgnylacetlc acld and Smtenng w f d 1 catalystare given in the following Table. The activity of mlnsat the catalyst inthe reduction of adiponitrile was assessed MP 11 v p I as m Examp 1eEXAMPLE 4 The method of Example 1 was repeated except-that thegranulated cobalt oxide'was mixed with 3% of its weight ComparatlveExample of p-toluic acid and sintering was effected for 15 mins. Apelleted, granulated cobalt oxide catalyst containing at 700 C. 3% ofglycerol tristearate as a sintering aid was prepared The physicalcharacteristics of the catalysts of Examples according to the method ofExample 3 except that sinter- 5 8 to 11 are given in the followingTable,

Catalyst Bulk Surface Pore Crush l Ex. density, area, volume, strength,Activity, No. Sintermg aid Other characteristics g./ml. mfl/g. mlJg.p.s.i. at sJl r 1 3% benzole acid 2.40 5.5 0.06 2 do 2. as 6.8 0.06 3%glyceryl tristearate 2. 09 9. 4 0.08 High 2.60 4.9 0.05 5% benzoic acid2% si ca 2.09 25.5 0. 09 3% glyceryl tristearata 1. 25. 4' '0. 09' 3%p-anisic acid 2. 30 4. 51 0.06 3% fumarie aci I 2.11 1. 35 0. 070 9 3%salieyclic acid 2.39 4. 20 0,064 l0 3% diphenyl acetic acid 1. 94 6. 3011. 3% p-toluic acid 2.34

5 What is claimed is: 1. A process for the manufacture of a sinteredcobalt oxide catalyst which comprises mixing cobalt oxide in particulateform with from 1 to 10% by weight of a carboxylic acid which is fumaricacid or a compound of the 5 formula R-CO H in which R is phenyl,p-methoxyphenyl, p-tolyl, o-hydroxyphenyl or diphenylmethyl, andsintering at a temperature above 500 C.

2. The process of Claim 1 in which the cobalt oxide and carboxylic acidis shaped prior to sintering.

3. The process of Claim 1 in which the cobalt oxide has incorporatedtherein from 0.1 to 0.5% by weight of silica to promote the activity ofthe catalyst.

6 References Cited UNITED STATES PATENTS l/l957 Jeflerson et al. 252459X 8/1966 Isacks et al 252-472 X US. Cl. X.R.

